HEALTH
TOBACCO AND ASTHMA FEATURE PETER DENOBLE
Asthma is considered a concern when it comes to fitness to dive because of associated airway reactiveness and obstruction of small airways, which may cause pulmonary barotrauma or drowning during diving. Preparticipation screening specifically addresses asthma; when divers admit to signs or symptoms, a medical evaluation by a physician is suggested. Guidelines for medical evaluations are provided by diving medical societies. On the other hand, tobacco smoking, which is a major cause of chronic obstructive pulmonary disease, is less stringently addressed in the Recreational Scuba Training Council (RSTC) screening questionnaire, and no specific guidelines are provided. Recently we have received questions about how respiratory function in people with asthma compares to respiratory function in people who smoke tobacco and how this affects the assessment of fitness to dive. OBSTRUCTIVE LUNG DISEASE Both asthma and smoking are associated with narrowing and inflammation of the small respiratory airways, which result in reduced airflow through pulmonary airways. However, 116 DIVERS FOR THE ENVIRONMENT | JUNE 2018
the reduced airflow with asthma occurs intermittently and is reversible whereas with chronic smoking airflow progressively and irreversibly deteriorates and usually doesn’t reveal itself until older age.With aging, about 20 percent of smokers and 23 percent of patients with asthma manifest chronic obstructive pulmonary disease (COPD) characterised by fixed airflow obstruction. Asthma most often presents at a young age as recurrent episodes of increased airway obstruction that may vary in frequency and intensity. In adulthood asthma attacks become less frequent. Adult-onset asthma occurs in individuals 20 years or older. This type of asthma is frequently caused by allergies. An asthma attack may be provoked by exercise, cold and dry air or inhalation of hypertonic aerosols (normal saline used diagnostically to provoke a reaction). The respiratory airways are affected by inflammation, hyperproduction of mucus and the contraction of muscles around them. Respiratory flow may be reduced by 10 to 20 percent in mild cases and 40 percent in severe cases. In some cases respiratory function appears normal, but challenge tests
cause hyperresponsiveness and reduced expiratory air flow. Narrowing of airways may be reversed by medications such as anti-inflammatories and bronchodilators. Anti-inflammatory medications such as inhaled steroids reduce swelling and mucus production in the airways. This relieves symptoms, improves airflow and makes airways less sensitive to provocative factors (cold, dry air, etc.). Asthma attacks may be stopped by bronchodilators – short-acting beta-agonists that relax bronchial muscles and open airways for easier air flow. Exerciseinduced asthma may be prevented by longlasting beta-agonists. People whose asthma is well controlled may lead normal lives that include exercise; they are less likely to experience an asthma attack while diving. Tobacco smoking affects breathing both chronically and acutely. Acute effects of smoking include increased carbon monoxide and reduced oxygen levels in the blood as well as paralysis of cilia in the airways, which impairs removal of mucus. Mucus can block terminal airways and cause overexpansion of alveoli during ascent from a dive, which puts a diver at risk for arterial gas embolism (AGE). In smokers
